For decades, the exterior of many residential and commercial buildings has been protected by "finishing" or "sheathing" materials including wood, metal, and polymer resins. Metal sheathing, such as aluminum siding, was at one point very popular, since it was more insect- and weather-resistent than wood siding, and could be anodized, painted, or laminated to provide a plurality of colors and styles. Metal sheathing also proved to be long lasting and energy efficient, but because it could not be easily sawed, clipped, or drilled with hand tools, it was relatively labor intensive to install. Additionally, metal sheathing materials had to be extremely thin to be cost efficient, and, because of their inherent lack of ductility, were susceptible to dents by minor impact loads.
In more recent times, "vinyl siding", (which is actually a resinous composition containing polyvinyl chloride), has provided a cheaper and more impact-resistant material for exterior siding panels. This material can also be provided in a wide variety of colors and patterns, but is more flexible and forgiving, and hence, will not deform plastically under minor impact loads. Thermoplastics, like polyvinyl chloride, are also easy to machine and cut and can be worked with almost any hand tool at the construction site.
It has been found, however, that vinyl siding has not always been satisfactory as an exterior sheathing material for irregular exterior wall surfaces. Do to earlier poor construction techniques, material inconsistency, or foundation settling, exterior walls in both new and old constructions are not always flat. Since vinyl siding, as opposed to metal siding, is very flexible, it usually conforms to the irregularities of the wall surface, resulting in a crooked, bowed, or unpleasing finish.
In order to compensate for this deficiency in vinyl siding, installers frequently must resort to using wooden shims which must be separately nailed to the support surface before the siding can be installed. Attempts have also been made to loosely nail the siding to the support surface so that the siding will "float" over the uneven portions of the exterior wall. In order to float the siding over the irregularities, but still provide a relatively straight and orderly appearance, the panel must be fairly rigid so as to span high and low points along the wall. Unfortunately, polyvinyl chloride, even in its most rigid state, only has a flexural modulus of about 0.5.times.10.sup.6 psi, and a tensile strength of about 1/7 of that of wrought aluminum.
Accordingly, there is a need for a thermoplastic-based siding panel that is more resistant to bending, or conforming to irregularities in exterior wall surfaces, but which retains its low cost and ability to be worked with ordinary hand tools at the construction site.